Urinals comprising a discharge trap formed at the bottom of a bowl portion for receiving a user's urine have been known for some time, as shown in Patent Document 1 (Japanese Published Unexamined Patent Application 2013-14965), Patent Document 2 (Japanese Published Unexamined Patent Application 2013-14964), and Patent Document 3 (Japanese Published Unexamined Patent Application 2011-214262). Such conventional discharge traps form a U shape having a descending pipe extending downward, a horizontal pipe gradually curving from the descending pipe and extending horizontally, and an ascending pipe similarly gradually curving from the horizontal pipe and extending upward.
To prevent the penetration of foul smells, etc. from discharge plumbing into the toilet space, a predetermined amount of flush water is constantly accumulated as pooled water at the bottom portion of the discharge trap; a water seal is formed by this pooled water.
When a user uses the urinal to urinate, urine flows into the discharge trap; the majority of the pooled water is discharged by the inflow of urine, and inside the discharge trap a liquid with a high urine concentration mixture of urine and water is present as pooled water. When flush water is flowed into the bowl portion after urination in order to flush the bowl portion after usage by a user, that flush water newly flows into the discharge trap; a liquid with a high urine concentration mixture of urine and water is discharged from the discharge trap, and is substituted by this newly inflowing flush water.
In the discharge trap, when the rate of substitution at which pooled water comprising a high urine concentration liquid is replaced by newly inflowing flush water (or the dilution rate at which pooled water comprising a high urine concentration liquid is diluted by newly inflowing flush water) is low, the urine concentration in post-replacement pooled water is high, and uric scale is known to more easily occur within the discharge trap. Note that the substitution rate is calculated based on how much of the urine-mixed fluid which had been accumulating in the trap prior to flushing is replaced by flush water.